Atrial fibrillation (AFib) affects about 6 million individuals in the USA and is a significant cause of morbidity and mortality. Percutaneous catheter intracardiac Radio Frequency Ablation (RFA) treatment of AFib requires contiguous transmural lesions between anatomical boundaries for effective durable electrical isolation. Current procedures have a ~50% recurrence rate, probably due to incomplete ablations and carry a ~4% risk of complications, primarily due to excessive RF energy deposition. Currently, there are no methods for intraoperative assessment of lesion formation and tissue characterization during intracardiac RFA. There is a clinical need for a system which will intraoperatively: 1) quantify electrical contact between electrode-tissue, 2) characterize tissue in electrode contact, distinguish ablated v/s non-ablated tissue (to identify gaps ablation lesions), 3) confirm and assess lesion formation e.g. lesion depth, extent of ablation, and 4) monitor rate of RF energy deposition in the tissue to enable titrate energy deposition in tissue, thus enable create contiguous transmural lesions safely. To address this clinical need; we have designed and prototyped an intraoperative High Frequency Dielectric Sensing RFA Monitoring and Lesion Assessment system (HFDS-RFA- LAS. Our solution involves; designing the ablation electrode of an RFA catheter as a ?miniature antenna? to monitor the electrical properties of the tissue adjacent to the antenna-electrode. The system comprises; a) ablation catheter with an antenna-electrode sensor, b) vector network analyzer to measure tissue dielectric properties in a frequency range of 10 MHz to 4 GHz, c) RF filter hardware to filter ablation (KHz) and measurement (MHz-GHz) frequencies and d) user interface/display to guide the procedure and monitor and assess lesion formation. To demonstrate proof-of-concept, we prototyped an RFA catheter with a front sensing antenna electrode, band selective RF filters and tested the system in swine (n=3, 21 lesions). By monitoring the high frequency reflection impedance electrical properties (HFRIEPs) of the antenna-electrode, the system intraoperatively monitors procedure parameters, characterizes tissue and assesses lesion formation with high certainty and accuracy. To advance this technology towards a clinical product; during Phase-I of this SBIR project; we will design and prototype a HFDS-RFA-LAS system comprising an 8.5-9.5 Fr steerable RFA catheter with an omnidirectional antenna electrode sensor, complete with saline flush irrigation and thermocouples and a high fidelity RF filter hardware to enable simultaneously ablate, sense and track catheter using clinical navigation and ablation hardware. The system will be tested in bench-top tests and in animals (n=7 swine) to quantitatively demonstrate feasibility of intraoperatively monitoring procedure parameters, characterizing tissue and assessing lesion formation.